Head-up display (HUD) systems are currently used in aircraft to provide pilots with essential information superimposed onto their forward field of view through the aircraft windshield. The information displayed by the HUD typically includes data in a symbolic format indicative of flight conditions, such as the operating conditions of the aircraft (e.g., attitude, airspeed, and altitude), or guidance information. HUD systems are also being designed for use in automobiles and other vehicles.
A typical HUD system includes a viewing element, called a combiner, that is placed in a pilot's forward field of view. The combiner is substantially transparent but is treated to be reflective to certain wavelengths of light. When symbolic information is projected onto the combiner from a relay lens using those wavelengths, the combiner refocuses the information at optical infinity and is overlaid on the pilot's forward field of view. A HUD system may therefore be advantageously used to provide information to the pilot in all phases of flight, but use of a HUD during take-off, landing, and taxi operations offer the greatest benefits.
Another technology that provides added situational awareness to an aircraft pilot is the use of imaging sensors. A sensor such as an IR-sensing or visible-sensing camera can provide real-time images of scenes of interest to the pilot. Imaging sensors are especially useful when the sensors are configured to sense non-visible radiation wavelengths. For example, runway lights may be detected in the near infra-red wavelength range even if inclement weather partially obscures lights from the pilot's view in the visible wavelength range. As another example, a sensor that detects visible light can be configured to detect a narrow range of wavelengths corresponding to emissions from a solid-state runway light such as an LED source. The output from IR-sensing or visible-sensing cameras have been provided to the pilot or co-pilot in a head-down display format. In this way the pilot and co-pilot can view the sensor output.
There has been some interest in combining images from an imaging sensor with HUD symbology on a HUD combiner such that the displayed image is conformal with, or overlays, a pilot's view through the windshield. Such a combination of situational technologies (HUD plus imaging sensor), known as an enhanced vision system or EVS systems, would further assist a pilot in guidance and navigation. Unfortunately, there are some situations where it is not feasible to install or use a complete HUD system. For example, some airplane cockpits may not have enough space in which to install a HUD combiner between the pilot and the aircraft windshield. The cost of a full HUD system also may be too expensive to install on some aircraft.
It is therefore an object of the invention to provide HUD symbology and imaging sensor outputs to a pilot of an aircraft where it is not feasible to provide a complete HUD system.
It is also an object of the invention to provide such symbology and outputs in a cost-effective manner.
It is a further object of the invention to provide an enhanced vision system that may be used with previously installed avionics equipment.
A feature of the invention is the simultaneous display of HUD symbology and images detected from imaging sensor on a head-down display in the aircraft.
An advantage of the invention is that enhanced vision system functionality may be provided in aircraft that are not able to install or use a complete HUD system.